Coated article with ir reflecting layer and method of making same

ABSTRACT

An IG window unit includes a coating supported by a glass substrate. The coating includes at least the following on the glass substrate moving from the glass substrate outwardly: at least one dielectric layer; a layer comprising zinc oxide; an infrared (IR) reflecting layer comprising silver; a layer comprising an oxide of Ni and/or Cr; an overcoat comprising a layer comprising tin oxide located over the oxide of Ni and/or Cr and a layer comprising silicon nitride.

This application relates to a coated article including an infrared (IR)reflecting layer of a material such as silver or the like. In certainexample embodiments, a layer comprising zinc oxide is provided under theIR reflecting layer in order to improve qualities thereof. In certainexample embodiments, the coating is a single-silver type coating, andincludes an overcoat including an uppermost layer of or includingsilicon nitride and a layer of or including tin oxide under the siliconnitride based layer, in certain example embodiments, the thicknesses ofthe silicon nitride based uppermost layer and the tin oxide based layerare balanced substantially equal, or equal plus/minus about 10-15%). ithas surprisingly been found that balancing the thicknesses of thesilicon nitride based uppermost layer and the adjacent tin oxide basedlayer results in an overall coating that has significantly improvedthermal cycling performance and improved mechanical durability. Incertain example embodiments, the silicon nitride based uppermost layerand the tin oxide based layer of the overcoat each have a thickness ofat least about 90 angstroms (Å), more preferably at least about 120 Å,and still more preferably at least about 150 Å. For example, the siliconnitride based uppermost layer and the tin oxide based layer may each befrom about 160-180 Å thick in certain example embodiments, so as toimprove thermal cycling performance and durability of the overallcoating, in certain example embodiments, the coating also hassurprisingly good substantially neutral film side reflective coloration,monolithically or more preferably in an insulating glass (IG) windowunit.

In certain example embodiments, an IG window unit including the coating(e.g., on surface #3) has an SHGC value of no less than about 0.65, morepreferably no less than about 0.68; and a visible transmission of atleast about 68%, more preferably at least about 70%, 72%, or even atleast about 74%. In certain example embodiments of this invention, theIG window unit can realize a combination of good visible transmission(T_(vis)) and an excellent solar heat gain coefficient (SHGC). In viewof the above, it is possible to permit the coated article, such as an IGwindow unit for example, to realize improved properties such as one ormore of a low U-value, and/or an Energy Rating (ER) of no less than 29.

Additionally, in certain example embodiments, it has surprisingly beenfound that the stress of the overcoat can be unexpectedly reduced byreducing nitrogen gas flow (N₂ ml/kW) and cathode power during thesputter-deposition process of the overcoat. It has been found that lowovercoat stress is a factor contributing to good thermal cyclingresults.

Background and Summary of Example Emobodiments of the Invention

Coated articles are known in the art for use in window applications suchas insulating glass (IG) window units, vehicle windows, monolithicwindows, and/or the like. In certain example instances, designers ofcoated articles often strive for a combination of high visibletransmission, substantially neutral color, low emissivity (oremittance), low sheet resistance (R_(s)), low U-values in the context ofIG window units, and/or low specific resistivity. High visibletransmission and substantially neutral color may permit coated articlesto be used in applications where these characteristics are desired suchas in architectural or vehicle window applications, whereaslow-emissivity (low-E), low sheet resistance, and low specificresistivity characteristics permit such coated articles to blocksignificant amounts of IR radiation so as to reduce for exampleundesirable heating of vehicle or building interiors.

However, conventional coated articles are lacking with respect to one ormore of: (i) thermal cycling performance, (ii) mechanical durability,(iii) ability to achieve good substantially neutral film side reflectivecoloration monolithically or more preferably in an insulating glass (IG)window unit, (iv) ability to realize a combination of good visibletransmission (T_(vis)) and an excellent solar heat gain coefficient(SHGC) and low U-values for increasing or maximizing solar heat gain andreducing or minimizing heat loss of building interiors, and/or (v)ability to meet an Energy Rating (ER) of no less than 29.

In view of the above, it will be appreciated that there exists a need inthe art for a coated article including a coating (e.g., in the contextof an IG window unit) which has the ability to realize one or more of:(i) improved thermal cycling performance, (ii) improved mechanicaldurability, (iii) substantially neutral film side reflective colorationmonolithically and/or more preferably in an insulating glass (IG) windowunit, (iv) high T_(vis) and good SHGC, (v) low U-values, and/or (vi) anEnergy Rating (ER) of no less than 29.

The Canadian Hydro-Quebec Energy Initiatives have asked for windowproduct for residential applications with high solar heat gain, highvisible light transmission, and good thermal insulation. In thisrespect, Zone C ER requires ER as high as 25, and Zone D requires ER noless than 29. Current conventional sputter-coated single Ag layercoatings in the market can meet some, but not all, requirements. Inparticular, they still need further energy rating improvement forresidential applications in northern climates mainly due to not having asufficiently high SHGC.

Certain example embodiments of this invention relate to a coated articleincluding an infrared (IR) reflecting layer of a material such as silveror the like. In certain example embodiments, a layer comprising zincoxide is provided under the IR reflecting layer in order to improvequalities thereof. In certain example embodiments, the coating is asingle-silver type coating, and includes an overcoat including anuppermost layer of or including silicon nitride and a layer of orincluding tin oxide immediately under and contacting the silicon nitridebased uppermost layer. In certain example embodiments, the thicknessesof the silicon nitride based uppermost layer and the tin oxide basedlayer of the overcoat are balanced (e.g., substantially equal, or equalplus/minus about 10%). It has surprisingly been found that balancing thethicknesses of the silicon nitride based layer and the adjacent tinoxide based layer results in a coating that has significantly improvedthermal cycling performance and improved mechanical durability. Incertain example embodiments, the silicon nitride based upper most layerand the adjacent tin oxide based layer each have a thickness of at leastabout 90 angstroms (Å), more preferably at least about 120 Å, and stillmore preferably at least about 150 Å. For example, the silicon nitridebased uppermost layer and the tin oxide based layer may each be fromabout 1 60-180 Å thick in certain example embodiments, so as to improvethermal cycling performance and durability of the coating. In certainexample embodiments, the coating also has surprisingly goodsubstantially neutral film side reflective coloration, monolithically ormore preferably in an insulating glass (IG) window unit. In certainexample embodiments, the thickness of the IR reflecting layer isadjusted to achieve a balance of low U-value and high SHGC formaximizing ER ratings.

In certain example embodiments, an IG window unit including the coating(e.g., on surface #3) has an SHGC value of no less than about 0.65, morepreferably no less than about 0.68; and a visible transmission of atleast about 68%, more preferably at least about 70%, 72%, or even atleast about 74%. In certain example embodiments of this invention, theIG window unit can realize a combination of good visible transmission(T_(vis)) and an excellent solar heat gain coefficient (SHGC). Forcoatings according to example embodiments of this invention, a high SHGCis preferred because the coating is adapted for use in northernclimates. The high SHGC desired for this coating is the opposite of lowSHGC values desired for coatings for use in southern climates. In viewof the above, it is possible to permit the coated article, such as an IGwindow unit for example, to realize improved properties such as one ormore of a low U-value (e.g., U-value of no greater than about 0.33, 0.30or 0.28), and/or an Energy Rating (ER) of no less than 25, morepreferably no less than 29.

Additionally, in certain example embodiments, it has been found that thestress of the overcoat can be dramatically reduced by increasing inertgas flow rate (e.g., argon gas flow), and reducing nitrogen gas flow (N₂ml/kW) and cathode power during the sputter-deposition process of theovercoat. It has been surprisingly found that low overcoat stress is asignificant factor contributing to good thermal cycling results.

In certain example embodiments, a layer comprising an oxide of Ni and/orCr is provided between the tin oxide based layer and the Ag based IRreflecting layer, and the layer comprising Ni and/or Cr may hesubstoichiometric in order to provide improved adhesion to the overlyingtin oxide based layer so as to improve durability. Coated articlesherein may be used in the context of insulating glass (IG) window units,or in other suitable applications such as monolithic windowapplications, laminated windows, and/or the like.

In certain example embodiments of this invention, there is provided acoated article including a coating supported by a glass substrate, thecoating comprising: at least one dielectric layer; a layer comprisingzinc oxide over the at least one dielectric layer; an infrared (IR)reflecting layer comprising silver on the glass substrate, located overand directly contacting the layer comprising zinc oxide, wherein thecoating includes only one IR reflecting layer; a layer comprising anoxide of Ni and/or Cr located over and directly contacting the IRreflecting layer comprising silver; an overcoat comprising a layercomprising tin oxide located over the oxide of Ni and/or Cr and a layercomprising silicon nitride located over and contacting the layercomprising tin oxide; and wherein, in the overcoat, the layer comprisingtin oxide and the layer comprising silicon nitride have substantiallyequal thicknesses plus/minus 15% in order to improve thermal cyclingperformance and mechanical durability of the coating.

In other example embodiments of this invention, there is provided amethod comprising: sputter-depositing at least one dielectric layer andat least one IR reflecting layer over at least the dielectric layer;sputter-depositing an overcoat on the glass substrate over at least theIR reflecting layer, the overcoat comprising a layer comprising tinoxide and a layer comprising silicon nitride located over and contactingthe layer comprising tin oxide; and when sputter-depositing the layercomprising silicon nitride using a nitrogen gas flow of no greater than450 sccm, using a cathode power of less than 50 kW, and using a ratio ofnitrogen gas flow to cathode power (N₂ ml/kW) of from about 6-10.

In yet another example embodiment of this invention, there is providedan IG window unit including a coating supported by a glass substrate,the coating from the glass substrate outwardly comprising: at least onedielectric layer; a layer comprising zinc oxide over the at least onedielectric layer; an infrared (IR) reflecting layer comprising silver onthe glass substrate, located over and directly contacting the layercomprising zinc oxide, wherein the coating includes only one IRreflecting layer; a layer comprising, an oxide of Ni and/or Cr locatedover and directly contacting the IR reflecting layer comprising silver;an overcoat comprising a layer comprising tin oxide located over theoxide of Ni and/or Cr and a layer comprising silicon nitride locatedover and contacting the layer comprising tin oxide; and wherein the IGunit has an SHGC value of at least 0.65, a visible transmission of atleast 70%, and an Energy Rating of at least 25.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a coated article according to anexample embodiment of this invention.

FIG. 2 is a cross sectional view of part of an insulating glass (IG)window unit including the coated article of FIG. 1 according to anexample embodiment of this invention.

FIG. 3 is a table illustrating optical and other characteristics of IGwindow units according to certain example embodiments of this invention.

FIG. 4 is a graph plotting the number of days until failure as afunction of nitrogen gas flow ml/kW during sputter deposition of theovercoat according to certain example embodiments of this invention.

FIG. 5 is a table illustrating the impact of process settings duringsputter deposition of an overcoat, for stress purposes, according tocertain example embodiments of this invention.

DETAILED DESCRIPTION OF EXAMPLE. EMBODIMENTS OF THE INVENTION

Referring now to the drawings in which like reference numerals indicatelike parts throughout the several views.

Coated articles herein may be used in applications such as monolithicwindows, IG window units such as residential windows, patio doors,vehicle windows, and/or any other suitable application that includessingle or multiple substrates such as glass substrates. Certain exampleembodiments of this invention are particularly adapted for residentialwindow and patio door applications where high heat gain and high visiblelight transmission is desired.

Generally speaking, certain example embodiments of this invention relateto a coated article including a coating 25 having an infrared (IR)reflecting layer 9 of a material such as silver, gold, or the like. Incertain example embodiments, a layer comprising zinc oxide 7 is providedunder the IR reflecting layer 9 in order to improve qualities of the Agbased layer 9. In certain example embodiments, the coating is asingle-silver type coating (only one Ag based IR reflecting layer 9 isprovided in the coating), and includes an overcoat (13, 15) including anuppermost layer 15 of or including silicon nitride and a layer of orincluding tin oxide 13 immediately under and contacting the siliconnitride based layer 15. The thicknesses (e.g., physical thicknesses) ofthe silicon nitride based layer 15 of the overcoat and the tin oxidebased layer 13 of the overcoat are balanced (e.g., substantially equal,or equal plus/minus about 15% or 10%). It has surprisingly been foundthat balancing the thicknesses of the silicon nitride based layer 15 andthe immediately adjacent tin oxide based layer 13 results in a coating25 that has significantly improved thermal cycling performance andimproved mechanical durability. In certain example embodiments, thesilicon nitride based uppermost layer 15 and the tin oxide based layer13 each have a thickness of at least about 90 angstroms (Å), morepreferably at least about 120 Å, and still more preferably at leastabout 150 Å. For example, the silicon nitride based uppermost layer 15and the adjacent tin oxide based layer 13 may each be from about 160-180Å thick in certain example embodiments, so as to improve thermal cyclingperformance and durability of the coating. In certain exampleembodiments, the coating also has surprisingly good substantiallyneutral film side reflective coloration, monolithically or morepreferably in an insulating glass (IG) window unit.

In certain example embodiments, an IG window unit (e.g., see FIG. 2)including the coating 25 (e.g., on surface #3) has an SHGC value of noless than about 0.65, more preferably no less than about 0.68; and avisible transmission of at least about 68%, more preferably at leastabout 70%, 72%, or even at least about 74%. In certain exampleembodiments of this invention, the IG window unit can realize acombination of good visible transmission (T_(vis)), excellent high solarheat gain coefficient (SHGC) and low U-value. For coatings according toexample embodiments of this invention, a high SHGC is preferred becausethe coating is adapted for use in northern climates. The high SHGCdesired for this coating is the opposite of low SHGC values desired forcoatings for use in southern climates. In view of the above, it ispossible to permit the coated article, such as an IG window unit forexample, to realize improved properties such as one or more of a lowU-value (e.g., U-value of no greater than about 0.33, 0.30 or 0.28),and/or an Energy Rating (ER) of no less than 29 (ER=57.76SHGC minus21.90 U-value minus 0.54 (L₇₅/A_(W)) +40; where L₇₅ is the total airflowrate in m³/h at a pressure difference of 75 Pa and A_(W) is the area inm² as per the known reference sizes per the Energy Star QualifyingCriteria for Residential Windows, door and Skylights in Canada Version2.0 4/1/05).

Additionally, in certain example embodiments, it has been found that thestress of the overcoat (13, 15) can be dramatically reduced by acombination of two or three of: (i) increasing argon (or other inertgas) flow rate, (ii) reducing nitrogen gas flow rate (N₂ ml/kW), and(iii) reducing cathode power, during the sputter-deposition process ofat least the silicon nitride inclusive layer 15 of the overcoat. It hasbeen surprisingly found that low overcoat stress is a factorcontributing to good thermal cycling results.

An example thermal cycling test is pursuant to TP-603-3, the disclosureof which is incorporated herein by reference. For example, anEnvirotronics Environmental Chamber, Model No. FLX900 may be used.Example settings for thermal cycling testing are as follows: thermalcycling, 11 hours at 23 degrees and 86% relative humidity, and 13 hoursat −17 degrees C. and 0% relative humidity (one cycle per twenty fourhours).

FIG. 1 is a cross sectional view of a coated article according to anexample embodiment of this invention. The coated article includes glasssubstrate 1 (e.g., clear, green, bronze, or blue-green glass substratefrom about 1.0 to 10.0 mm thick, more preferably from about 1.0 mm to6.0 mm thick), and a multi-layer coating (or layer system) 25 providedon the substrate 1 either directly or indirectly. As shown in FIG. 1,the coating 25 is of or includes dielectric layer 2 of or includingsilicon nitride (e.g., Si₃N₄, or some other suitable stoichiometry),dielectric layer 3 of or including a metal oxide such as an oxide oftitanium (e.g., TiO_(x) where “x” is from 1 to 2, more preferably about2), dielectric layer 5 of or including silicon nitride Si₃N₄, or someother suitable stoichiometry), zinc oxide inclusive contact layer 7(e.g., ZnO, where “x” may be about 1; or ZnAl_(x)O), IR (infrared)reflecting layer 9 including or of silver, gold, or the like, uppercontact layer 11 of or including an oxide of Ni and/or Cr (e.g.,NiCrO_(x)), and an overcoat of or including tin oxide inclusivedielectric layer 13 and silicon nitride inclusive dielectric layer 15.Of course, the silicon nitride inclusive layer 15 may further includeAl, oxygen, or the like, and the tin oxide layer 13 may likewise furtherinclude other materials such as nitrogen, zinc, or the like. Otherlayers and/or materials may also be provided in the coating 25 incertain example embodiments of this invention, and it is also possiblethat certain layers may be removed or split in certain exampleinstances. Moreover, one or more of the layers discussed above may bedoped with other materials in certain example embodiments of thisinvention.

In monolithic instances, the coated article includes only one substratesuch as glass substrate 1 (see FIG. 1). However, monolithic coatedarticles herein may be used in devices such as IG window units forexample. Typically, as shown in FIG. 2, an IG window unit may includetwo spaced apart substrates 1 and 2, with an air gap 4 definedtherebetween. Example IG window units are illustrated and described, forexample, in U.S. Pat. Nos. 5,770,321, 5,800,933, 6,524,714, 6,541,084and US 2003/0150711, the disclosures of which are all herebyincorporated herein by reference. An example IG window unit as shown inFIG. 2 may include, for example, the coated glass substrate 1 shown inFIG. 1 coupled to another glass substrate 2 via spacer(s), sealant(s) orthe like with a gap 4 being defined therebetween. This gap 4 between thesubstrates in IG unit embodiments may in certain instances be filledwith a gas such as argon (Ar). An example IG unit may comprise a pair ofspaced apart substantially clear glass substrates each about 3-4 mmthick one of which is coated with a coating 25 herein in certain exampleinstances, where the gap 4 between the substrates may be from about 5 to30 mm, more preferably from about 10 to 20 mm, and most preferably about12-16 mm. In certain example instances, the coating 25 may be providedon the side of the inner glass substrate 1 facing the gap, i.e., surface#3 (although the coating may be on the other substrate in certainalternative embodiments). In other example embodiments, the IG windowunit may include additional glass sheets (e.g., the IG unit may includethree spaced apart glass sheets instead of two).

Still referring to FIG. 2, in certain example IG unit embodiments ofthis invention, the coating 25 is designed such that the resulting IGunit with, for reference purposes, a pair of 3-4 mm clear glasssubstrates spaced apart by 12-16 mm with Ar gas in the gap) has aU-value (imperial, winter, emissivity. Rs) of no greater than 0.31, morepreferably no greater than 0.30, 0.29 or 0.28 Btu/h ft F. It is possiblefor the coating 25 to be provided on the interior surface of the otherglass substrate 2 in alternative embodiments of this invention.

Silicon nitride inclusive dielectric layers 2 and 5 are provided forantireflection purposes, and have been found to allow color shifts to bereduced. One or both of the silicon nitride layers 2 and/or 5 may beSi₃N₄. Alternatively, one or both of the silicon nitride layers 2 and/or5 may be of the Si-rich type (not fully stoichiometric). Moreover, oneor both of the silicon nitride layers 2 and/or 5 may further include adopant such as aluminum or stainless steel, and/or small amounts ofoxygen. These layers may be deposited via sputtering in certain exampleembodiments, or via any other suitable technique.

Dielectric layer 3 may be of or include titanium oxide in certainexample embodiments of this invention. The titanium oxide of layer 3 mayin certain example instances be represented by TiO_(x), where x is from1.5 to 2.5, most preferably about 2.0. The titanium oxide may bedeposited via sputtering or the like in different embodiments. Incertain example instances, dielectric layer 3 may have an index ofrefraction (n), at 550 nm, of at least 2.0, more preferably of at least2.1, and possibly from about 2.3 to 2.6 when the layer is of or includestitanium oxide. In certain embodiments of this invention, the thicknessof titanium oxide inclusive layer 3 is controlled so as to allow a*and/or b* color values (e.g., transmissive, film side reflective, and/orglass side reflective) to be fairly neutral (i.e., close to zero) and/ordesirable. Other materials may be used in addition to or instead oftitanium oxide in certain example instances. In certain alternativeembodiments, the Ti in oxide layer 3 may be replaced with another metalso that layer 3 may be of or include another metal oxide or dielectricincluding but not limited to tin oxide, zinc oxide, zinc aluminum oxideor silicon nitride.

Dielectric contact layer 7 is of or includes zinc oxide (e.g., ZnO). Thezinc oxide of layer(s) 7 may contain other materials as well such as Al(e.g., to form ZnAlO_(x)) in certain example embodiments. For example,in certain example embodiments of this invention, zinc oxide layer 7 maybe doped with from about 1 to 10% Al (or B), more preferably from about1 to 5% Al (or B), and most preferably about 2 to 4% Al (or B). The useof zinc oxide 7 under the silver in layer 9 allows for an excellentquality of silver to be achieved. In certain example embodiments (e.g.,to be discussed below) the zinc oxide inclusive layer 7 may be foiinedvia sputtering a ceramic ZnO or metal rotatable magnetron sputteringtarget. It has been found that the use of the ceramic target in certainexample embodiments (e.g., of ZnO, which may or may not be doped withAl, F or the like) allows for a high quality of silver to be providedthereby resulting in a lower emissivity coating. While the Zn:O in theceramic target maybe stoichiometric in certain example embodiments, atleast one substoichiometric ceramic target comprising ZnO_(x) (e.g.,where 0.25≦x≦0.99, more preferably 0.50≦x≦0.97, and even more preferably0.70≦x≦0.96) may instead be used in sputter-depositing a zinc oxideinclusive layer 7 which may be substoichiometric in certain instances.

Infrared (IR) reflecting layer 9 is preferably substantially or entirelymetallic and/or conductive, and may comprise or consist essentially ofsilver (Ag), gold, or any other suitable IR reflecting material. IRreflecting layer 9 helps allow the coating to have low-E and/or goodsolar control characteristics such as low emittance. low sheetresistance, and so forth. The IR reflecting layer may, however, beslightly oxidized in certain embodiments of this invention.

The silver based layer 9 is not very thick in certain exampleembodiments of this invention. The rather thin nature of the silverbased layer 9 leads to bad durability characteristics. This iscompensated for according to certain example embodiments of thisinvention by balancing the two layers 13 and 15 of the overcoat asdiscussed herein. Thus, the silver based IR reflecting layer 9 may bethinned, without sacrificing durability of the coating.

The upper contact layer 11 may be of or include an oxide of Ni and/orCr. In certain example embodiments, upper contact layer 11 may be of orinclude nickel (Ni) oxide, chromium/chrome (Cr) oxide, or a nickel alloyoxide such as nickel chrome oxide (NiCrO_(x)), or other suitablematerial(s). The use of, for example, NiCrO_(x) in this layer(s) 11allows durability to be improved. The NiCrO_(x) layer(s) 11, 11 may befully oxidized in certain embodiments of this invention (i.e., fullystoichiometric), or alternatively may only be partiallyoxidized—substoichiometric (before and/or after optional HT). In certaininstances, the NiCrO_(x) layer 11 may be at least about 50% oxidized.Contact layer 11 (e.g., of or including an oxide of Ni and/or Cr) may ormay not be oxidation graded in different embodiments of this invention.Oxidation grading means that the degree of oxidation in the layerchanges through the thickness of the layer so that for example a contactlayer may he graded so as to he less oxidized at the contact interfacewith the immediately adjacent IR. reflecting layer 9 than at a portionof the contact layer further or more/most distant from the immediatelyadjacent IR reflecting layer. Descriptions of various types of oxidationgraded contact layers are set forth in U.S. Pat. No. 6,576,349, thedisclosure of which is hereby incorporated herein by reference. Contactlayer 11 (e.g., of or including an oxide of Ni and/or Cr) may or may notbe continuous in different embodiments of this invention across theentire IR reflecting layer 9.

It have been found that using a layer comprising an oxide of Ni and/orCr 11 that is substoichiometric (metal rich) provides improved adhesionto the overlying tin oxide based layer 13 so as to improve durability ofthe overall coating. Thus, the use of a substoichiometric layercomprising an oxide of Ni and/or Cr for upper contact layer 11 isadvantageous in this respect.

The overcoat is of or includes dielectric layers 13 and 15 in certainexample embodiments. Dielectric layer 13 may be of or include a metaloxide such as tin oxide in certain example embodiments of thisinvention. Metal oxide inclusive layer 13 is provided for antirefiectionpurposes, and also improves the emissivity of the coated article and thestability and efficiency of the manufacturing process. The tin oxidelayer 13 may be doped with other materials such as nitrogen and/or zincin certain example embodiments of this invention. The tin oxide basedlayer 13 provides good durability and improves light transmission.Dielectric layer 15 may be of or include silicon nitride (e.g., Si₃N₄ orother suitable stoichiometry) or any other suitable material in certainexample embodiments of this invention such as silicon oxynitride.Silicon nitride layer 15 may further include other material, such asaluminum as a dopant or small amounts of oxygen in certain exampleembodiments of this invention. Optionally, other layers may be providedabove layer in the overcoat in certain example instances. Layer 15 isprovided for durability purposes, and to protect the underlying layers.In certain example embodiments, silicon nitride based layer 15 may havean index of refraction (n) of from about 1.9 to 2.2, more preferablyfrom about 1.95 to 2.05. In certain example embodiments, Zr may heprovided in the silicon nitride of layer 15 (or layer 2 or layer 5).Thus, one or more of layers 2, 5 and/or 15 may be of or include SiZrNxand/or zirconium oxide in certain example embodiments of this invention.

Other layer(s) below or above the illustrated coating 25 may also beprovided. Thus, while the layer system or coating is “on” or “supportedby” substrate 1 (directly or indirectly), other layer(s) may be providedtherebetween, Thus, for example, the coating of FIG. 1 may he considered“on” and “supported by” the substrate 1 even if other layer(s) areprovided between layer 3 and substrate 1. Moreover, certain layers ofthe illustrated coating may be removed in certain embodiments, whileothers may be added between the various layers or the various layer(s)may be split with other layer(s) added between the split sections inother embodiments of this invention without departing from the overallspirit of certain embodiments of this invention. For example and withoutlimitation, silicon nitride layer 5 may be removed and layer 3 may be oftin oxide (e.g., SnO₂) instead of titanium oxide in certain alternativeembodiments of this invention. As another example, silicon nitride layer2 may be removed and layer 5 may be of tin oxide (e.g., SnO₂) instead ofsilicon nitride in certain alternative embodiments of this invention. Asyet another example, layer 5 may be of tin oxide (e.g., SnO₂) instead ofsilicon nitride in still further alternative embodiments of thisinvention.

While various thicknesses may be used in different embodiments of thisinvention, example thicknesses and materials for the respective layerson the glass substrate 1 in the FIG. 1 embodiment are as follows, fromthe glass substrate outwardly (e.g., the Al content in the zinc oxidelayer and the silicon nitride layers may be from about 1-10%, morepreferably from about 1-3% in certain example instances):

TABLE 1 (Example Materials/Thicknesses; FIG. 1 Embodiment) PreferredMore Layer Range ({acute over (Å)}) Preferred ({acute over (Å)}) Example(Å) Si_(x)N_(y) (layer 2) 20-300 Å 60-160 Å 135 Å  TiO_(x) (layer 3)30-200 {acute over (Å)} 40-120 {acute over (Å)} 95 Å Si_(x)N_(y) (layer5) 20-300 Å 40-140 Å 65 Å ZnAlO_(x) (layer 7) 10-200 {acute over (Å)}40-420 {acute over (Å)} 90 Å Ag (layer 9) 40-120 {acute over (Å)}  65-95{acute over (Å)} 85 Å NiCrO_(x) (layer 11)  10-70 {acute over (Å)} 20-50 {acute over (Å)} 30 Å SnO₂ (layer 13) 80-210 Å 160-180 Å  170 Å Si_(x)N_(y) (layer 15) 100-250 {acute over (Å)}  160-180 {acute over(Å)}  170 Å 

In certain example embodiments of this invention, coated articles herein(e.g., see FIG. 1) may have the following low-E (low emissivity), solarand/or optical characteristics set forth in Table 2 when measuredmonolithically, absent any heat treatment (th erm al tempering).

TABLE 2 Low-E/Solar Characteristics (Monolithic; non-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=11.0 <=10 <=9E_(n): <=0.2 <=0.15 <=0.11 T_(vis) (%): >=70 >=80 >=85

Moreover, IG window units having coated articles according to certainexample embodiments of this invention have the following opticalcharacteristics (e.g., where the coating 25 of FIG. 1 is used in the IGunit of FIG. 2) (e.g., for purposes of reference, when the coating isprovided on a clear soda lime silica glass substrate from 1 to 10 mmthick, preferably about 3-4 mm thick) on surface #3 of an IG window unitabsent any HT of the coating. The good film side (or “outside”)reflective color values (fairly neutral) are noted.

TABLE 3 Example Optical Characteristics (IG Unit) Characteristic GeneralMore Preferred T_(vis) (or TY)(Ill. C., 2 deg.): >=70% >=74.5%   a*_(t)(Ill. C., 2°): −3.0 to +1.0 −2.0 to 0.0  b*_(t) (Ill. C., 2°): −1.0 to+4.0  0.0 to +2.0 R_(outside)Y (Ill. C., 2 deg.): <=18% <=14% a*_(out)(Ill. C., 2°): −5.0 to +1.0  −4 to 0.0 b*_(out) (Ill. C., 2°): −2.0 to+4.0 −1.0 to +2.5 R_(inside)Y (Ill. C., 2 deg.): <=15% <=13% a*_(inside)(Ill. C., 2°): −7.0 to +4.0 −5.5 to +2.0 b*_(inside) (Ill. C., 2°): −5.0to +5.0 −3.0 to +0.5 SHGC:  >=.65    >=.68 Energy Rating(ER): >=25    >=29 U-value (Btu/h ft F): <=0.33 <=0.30 or 0.28

EXAMPLES

The following example is provided for purposes of example only, and isnot intended to be limiting. The following Example 1 was made viasputtering so as to have approximately the layer stack set forth below,from the clear glass substrate outwardly. The listed thicknesses areapproximations:

TABLE 4 Layer Stack for Example 1 Layer Thickness (angstroms) GlassSubstrate   3 mm Si₃N₄ 135 {acute over (Å)}  TiO_(x) 95 {acute over (Å)}Si₃N₄ 65 {acute over (Å)} ZnAlO_(x) 90 {acute over (Å)} Ag 85 {acuteover (Å)} NiCrO_(x) 30 {acute over (Å)} SnO₂ 170 Å  Si₃N₄ 170 {acuteover (Å)} 

The two layers 13 and 15 of the overcoat were sputter-deposited to thesame thickness. After being sputter deposited onto the glass substrate,the coated article of Example 1 (see also FIG. 1) was provided in an IGwindow unit as shown in FIG. 2 so that the coating 25 was on surface 43of the IG unit. The characteristics of Example 1 are shown in FIG. 3.

Example 2 was the same as Example 1, except that layer 5 was not presentin Example 2, silicon nitride layer 2 was 140 angstroms thick, and layer3 was made of tin oxide instead of titanium oxide and was about 170angstroms thick, The characteristics of Example 2 are also shown in FIG.3.

Example 3 was the same as Example 1, except that silicon nitride layer 2was about 135 angstroms thick, titanium oxide layer 3 was about 45angstroms thick, and layer 5 was made of tin oxide instead of siliconnitride and was about 100 angstroms thick. The characteristics ofExample 3 are also shown in FIG. 3.

Referring to FIG. 4, it has been found that balancing the thicknesses ofthe silicon nitride based layer 15 and the immediately adjacent tinoxide based layer 13 results in a coating 25 that has significantlyimproved thermal cycling performance and improved mechanical durability.In FIG. 4, “Top Sn/SiOC” refers to the overcoat (OC) of tin oxide 13 andsilicon nitride 15, and the numbers such as 100, 240, 145, 195 and 170in FIG. 4 refer to thicknesses of the corresponding layers of theovercoat in angstroms. FIG. 4 illustrates that the number of days untilfailure of a thermal cycling test is increased when the thicknesses ofthe layers 13 and 15 are balanced (substantially equal to each other).In certain instances, good results may also be achieved when the tinoxide based layer 13 is from about 0-25% thicker than the siliconnitride based layer 15, more preferably from about 1-20% or 1-15%thicker. The thicknesses (e.g., physical thicknesses) of the siliconnitride based layer 15 of the overcoat and the tin oxide based layer 13of the overcoat are balanced (e.g., substantially equal, or equalplus/minus about 15% or 10%) in certain example embodiments. In certainexample embodiments, the silicon nitride based uppermost layer 15 andthe tin oxide based layer 13 each have a thickness of at least about 90angstroms (Å), more preferably at least about 120 Å, and still morepreferably at least about 150 Å. For example, the silicon nitride baseduppermost layer 15 and the adjacent tin oxide based layer 13 may each befrom about 160-210 or 160-180 Å thick in certain example embodiments, soas to improve thermal cycling performance and durability of the coating.In certain example embodiments, the average stress of the siliconnitride based layer 15 is less than about 400 MPa, more preferably lessthan about 300 MPa. In certain example embodiments, the average stressof the tin oxide based layer 13 is less than about 350 MPa, morepreferably less than about 300 or 250 MPa.

FIG. 5 is a table illustrating that the design of the overcoat (layers13, 15) are adjusted/provided in order to achieve good thermal cyclingtest results. It is believed that good thermal cycling performance isuseful for the coating to endure outdoor temperature and humidityswings, especially in northern climates. In particular, in certainexample embodiments, it has been found that the stress of the overcoat(13; 15) can be dramatically reduced by reducing nitrogen gas flow andcathode power (N₂ ml/kW) during the sputter-deposition process of atleast the silicon nitride inclusive layer 15 of the overcoat. It hasbeen surprisingly found that low overcoat stress (average MPa) is asignificant factor contributing to good thermal cycling results. It canbe seen from FIG. 4 that the stress of the silicon nitride based layer15 can be reduced by providing (i) a ratio of nitrogen gas flow tocathode power (N₂ ml/kW) of from about 6-10, more preferably from about7-9, in combination with (ii) the use of cathode power during sputteringof less than 50, more preferably less than 45, even more preferably lessthan 40, and most preferably less than about 35 or even 30 kW, and (iii)nitrogen gas flow rate (sccm) of no greater than about 450, 400, 350 or300 sccm. When this nitrogen gas flow to cathode power ratio (N₂ ml/kW)is used, it can be seen in FIG. 5 that stress in the layer 15 becomessmaller as the cathode/target power (kW) becomes smaller along with thenitrogen gas flow rate. This is advantageous because low stress in theovercoat improve thermal cycling performance of the coating. However,the coating 25 formed by sputter-depositing using reduced nitrogen gasflow and reduced cathode power (N₂ ml/kW) during at least the formationof the silicon nitride based layer 15 may have deteriorated mechanicaldurability. It has been surprisingly found that with a preferredthickness range of overcoat design (13, 15), the overall coating 25 canhave both good thermal cycling performance and mechanical durability.This is a surprising and unexpected result.

In a similar manner, FIG. 5 also illustrates that stress in the tinoxide based layer 13 can be reduced by reducing the cathode/target powerused during sputter-depositing that layer. In certain exampleembodiments, the stress in layer 13 is reduced when the cathode powerused to sputter-depositing the tin oxide based layer 13 is no more than55, more preferably no more than 53 sccm.

It has also been found that increasing argon gas flow during sputteringof the silicon nitride based layer 15 and/or the tin oxide based layer13 can be helpful in improving durability. For example, the siliconnitride based layer 15 is sputter-deposited using an argon gas flow ofat least about 300 sccm, more preferably at least about 350 sccm, andmost preferably at least about 375 sccm.

While the invention has been described in connection with what ispresently considered to he the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

This listing of claims will replace all prior versions, and listings, ofclaims in the application: 1-11. (canceled)
 12. An IG window unitincluding a coating supported by a glass substrate, the coating from theglass substrate outwardly comprising: at least one dielectric layer; alayer comprising zinc oxide over the at least one dielectric layer; aninfrared (IR) reflecting layer comprising silver on the glass substrate,located over and directly contacting the layer comprising zinc oxide,wherein the coating includes only one IR reflecting layer; a layercomprising an oxide of Ni and/or Cr located over and directly contactingthe IR reflecting layer comprising silver; an overcoat comprising alayer comprising tin oxide located over the oxide of Ni and/or Cr and alayer comprising silicon nitride located over and contacting the layercomprising tin oxide; and wherein the IG unit has an SHGC value of atleast 0.65, a visible transmission of at least 70%, and an Energy Ratingof at least
 25. 13. The IG unit of claim 12, wherein the IG unit has anSHGC value of at least 0.68, a visible transmission of at least 74.5%,and an Energy Rating of at least
 29. 14. The IG unit of claim 12,wherein the IG unit has a U-value of no greater than 0.30 Btu/h ft F.15. The IG unit of claim 12, wherein said glass substrate is an interiorglass substrate, the IG unit further comprising an exterior glasssubstrate located adjacent an exterior of a building in which the IGunit is provided, wherein the coating is provided on a surface of theinterior glass substrate facing a gap between the interior and exteriorglass substrates, and wherein the IG unit has, as viewed from anexterior of the building, a reflective a* value of from about −4 to −0and a reflective b* value of from about −1 to +2.5. 16-20. (canceled)